WO1999011681A1

WO1999011681A1 - Latex based on hydrophobic polymer core/shell structures film forming at low temperature without coalescent agent

Info

Publication number: WO1999011681A1
Application number: PCT/FR1998/001859
Authority: WO
Inventors: Fabrice Domingues Dos Santos; Xavier Drujon; Pascale Fabre; Ludwik Leibler; Gilles Meunier
Original assignee: Elf Atochem S.A.
Priority date: 1997-08-28
Filing date: 1998-08-27
Publication date: 1999-03-11
Also published as: EP1007578B1; EP1007578B2; AU9079698A; DE69819520D1; ES2210812T5; ATE253600T1; US6723779B2; CN1136244C; CN1275138A; DE69819520T3; FR2767835A1; CA2302474A1; DE69819520T2; FR2767835B1; US20020132055A1; JP2001514312A; US6531185B1; ES2210812T3; CA2302474C; EP1007578A1

Abstract

The invention concerns hydrophobic films for coating surfaces obtained by drying at low temperature, not requiring coalescent agents, latex containing a core-structured polymer with soft characteristic having a glass transition temperature lower than 20 °C enclosed in a shell with hard characteristic having a glass transition temperature higher than 50 °C.

Description

LATEX BASED ON HYDROPHOBIC POLYMERS LOW TEMPERATURE CORE / BARK STRUCTURES WITHOUT COALESCING AGENTS

The invention relates to the field of surface treatment and in particular to hydrophobic thermoplastic films for surface coatings and more particularly to films obtained by drying at low temperature of a latex containing neither volatile organic compounds nor coalescing agents.

For the purposes of the invention, the term “latex” means an aqueous dispersion of polymer particles such as can be obtained by emulsion polymerization of one or more monomers.

Many latexes are intended for the building, paper, textile, leather industries and are used in the surface treatments of various materials in particular like paint, varnish, glue, putty. In general, such latexes are required to have a minimum filming temperature, hereinafter referred to as TMF, the lowest possible. TMF is the lowest temperature at which particles form a continuous film after evaporation of water.

When the polymers constituting the particles in dispersion of a latex have a relatively low glass transition temperature, designated by Tg, the filmification of the latex at room temperature is easy but the films obtained are tacky and of poor mechanical strength. On the other hand, if the polymers have a high Tg the films will be of better quality but the filmification at room temperature would require the addition of a coalescing agent. The latter is generally a volatile organic compound which evaporates during the application and the formation of the film, as described in USP 4,455,402 and USP 5,021,469.

For obvious reasons of respect for the environment and cost reduction, it is sought to develop latexes containing neither volatile organic compounds nor coalescing agents, having a relatively low TMF and being able to give films at room temperature without tacky. superficial and of good mechanical quality.

To achieve this objective, EP 466 409 proposes a solution based on a mixture of two latexes, one at low Tg generally qualified as "soft" bringing the filmification the other at high Tg generally qualified as "hard" providing mechanical strength. USP 263 193 describes a solution based on a bark / heart latex with a bark of a "soft" character and a heart of a "hard" character. Unlike the previous document, EP 609 756 describes a latex prepared in two stages having a "soft" core of Tg ranging from -5 ° C to -55 ° C and a "hard" shell of Tg less than 50 ° C .

Likewise FR 2 090 483 describes a latex, obtained by polymerization in two stages, consisting of 35 to 50% by weight of a polymer obtained in the first stage having a Tg of less than 10 ° C. and from 50 to 65% of a polymer with a Tg greater than 60 ° C. obtained in the second stage, the first stage polymer being crosslinked and fixed in the second.

The Applicant has found that an ingenious solution to the problem described above resides in a latex containing particles of hydrophobic polymers structured in the core / shell. With a core called "soft" having a Tg of less than 20 ° C and a bark called "hard" having a Tg of more than 50 ° C. Indeed, the Applicant has discovered that, provided that the mass participation of the bark in the total weight of the polymer particles does not exceed 30%, such a latex applied to any surface gives, after drying at low temperature, and without the intervention of coalescing agents or volatile organic compounds, a continuous film, structured in the form of soft parts dispersed in a hard, homogeneous matrix, without surface tack and having good mechanical strength.

In general, hydrophobicity is the insolubility in water or the absence of affinity with water. According to the invention, this lack of affinity can be prioritized. Indeed, the hydrophobicity according to the invention is defined by the solubility parameter (delta) as described in "properties of polymers" by DW Van Krevelen, 1990 third edition p 220. This parameter makes it possible to classify the different polymers according to their affinities vis-à-vis water. According to the invention, a polymer is hydrophobic if its (delta) is less than 26. In addition if (deltal) of a polymer 1 is less than (delta2) of a polymer 2 then 1 is more hydrophobic than 2.

One of the objects of the invention is a hydrophobic thermoplastic film consisting of 70 to 90% by weight of a polymer (P1) with a soft character having a Tg of less than 20 ° C. dispersed in 10 to 30% of a polymer (P2 ) with a hard character having a Tg greater than 50 ° C.

The polymer P1 is dispersed in the form of individualized nodules in the matrix constituted by the polymer P2.

The film of the invention is hydrophobic within the meaning of the invention defined above, moreover P1 is more hydrophobic than P2. Preferably, P1 has a Tg of less than 0 ° C and P2 a Tg of more than 60 ° C.

The film of the invention can be characterized by two distinct techniques. The first is transmission electron microscopy of which an example corresponding to the invention is given in FIG. 1. A section of 80 nm in thickness of a film is marked using a reagent specific to the polymer P1. This appears in dark while the polymer P2 appears in light. In FIG. 1, it can be seen without difficulty that the structure of the film is indeed that described above, that is to say individualized nodules of P1 dispersed in a continuous matrix of P2. The second technique is dynamic thermomechanical analysis (DMA), an example of which corresponds to the film previously described is given in Figure 2. This shows that tangent delta has two peaks characteristic of the presence of two distinct phases in the material. On the other hand, the measurement of a Young's modulus, E 'at room temperature greater than 1 E8 Pa shows that the film does not have a surface tack and that taking into account the respective proportions of polymers P1 and P2 in the film it is the polymer P2 (hard) which constitutes the continuous phase.

The polymers forming the films of the invention can be prepared by emulsion polymerization in two stages as described below and consist essentially of units derived by polymerization of monomers chosen from group I consisting of:

- C1 -C8 (meth) acrylic acid esters

- vinyl esters of linear or branched carboxylic acids such as vinyl acetate, vinyl stearate.

- styrene and its derivatives such as chloro methyl styrene, alpha methyl styrene ...

- conjugated dienes such as butadiene, isoprene

- acrylamide, methacrylamide and acrylonitrile

- vinyl chloride

- (meth) acrylic acids and their derivatives, such as omhydrides. The selection of monomers for both the soft polymer and the hard polymer is conditioned by the properties such as hydrophobicity, Tg, which it is desired to confer on the polymer in question. For example :

The Tg of a polymer can be estimated a priori by the law of FOX

1 / Tg = wa / Tg (a) + wb / Tg (b) + .... where w (a) and w (b) are the mass fractions of monomers a and b, Tg (a) and Tg (b ) are the glass transitions of homopolymers correspondents. Tg (a) and Tg (b) are taken from literature such as the "Polymer handbook" 3rd edition, 1989.

For each polymer to be prepared the monomer or the nature and the composition of the mixture of monomers when it is several monomers are determined so as to obtain the desired Tg.

Thus, to prepare the polymer with a "hard" character, the mixture of monomers to be polymerized can consist mainly of at least one monomer chosen from the group consisting of: methyl methacrylate, styrene and vinyl chloride.

Likewise for the polymer with a "soft" character, the mixture of monomers can consist mainly of at least one monomer chosen from the group consisting of butyl acrylate, butadiene and isoprene.

The soft and hard parts can be crosslinked by means of monomers having at least two copolymerizable double bonds. These monomers can be chosen from group II consisting of: a) conjugated dienes, such as butadiene and isoprene b) allyl esters of unsaturated alpha beta carboxylic or dicarboxylic acids, such as allyl acrylate, methacrylate d allyl or diallyl maleate c) polyacrylics or polymethacrylics such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butanediol diacrylate, pentaerγthritol tetraacrylate d) polyvinylics divinylbenzene or trivinyl benzene e) polyallylics such as triallyl cyanurate or triallyl trimesate. Preferably, only the heart is crosslinked. The preferred crosslinking monomers according to the invention are butadiene and 1,4-butanediol diacrylate. The content of crosslinking monomers is between 0 and 10% by weight of the total weight of the particles.

The "hard" part can be grafted onto the "soft" part by the introduction onto the latter of residues of monomer units. These residues of monomer units are obtained by the incorporation in the "soft" part of grafting monomers chosen either from group II a) of conjugated dienes, the residues of monomer units resulting from the partial incorporation in 1, 2 of the diene during from polymerization, either from group II b) allyl esters of alpha beta unsaturated carboxylic or dicarboxylic acids, which have two copolymerizable functions with different reactivity.

The preferred grafting monomers according to the invention are butadiene, allyl methacrylate and diallyl maleate. The content of grafting monomers is between 0 and 10% by weight of the total weight of the particles.

One of the means of obtaining the films of the invention is the drying at low temperature, without the help of either coalescing agents or other volatile organic compounds, of a latex whose particles are structured in the core / shell.

Another subject of the invention is a latex containing neither coalescing agents nor volatile organic compounds, film-forming by evaporation at a temperature below 40 ° C and preferably close to 25 ° C, said latex being based on polymer particles hydrophobic structured in heart / bark consisting of:

70 to 90% by weight of at least one polymer with a soft character having a Tg of less than 20 ° C. forming the core, and

- 10 to 30% by weight of at least one hard polymer having a Tg greater than 50 ° C forming the shell.

Preferably the core has a Tg of less than 0 ° C and the shell a Tg of more than 60 ° C. In addition, and within the meaning of the invention, the heart is more hydrophobic than the bark.

The latexes of the invention are prepared in two stages, by emulsion polymerization of a mixture of monomers consisting of: from 90% to 100% by weight of at least one monomer chosen from group I, and from 0% to 10 % by weight of at least one monomer chosen from group II.

In general, the latexes of the invention are prepared by emulsion polymerization in at least two stages according to the polymerization techniques well known to those skilled in the art.

The composition of the mixture of monomers to be polymerized at each stage depends on the character which it is desired to give to the polymer formed in this stage (Tg, hydrophobicity).

According to the invention, in a first step, the polymer with a "soft" character and a Tg of less than 20 ° C. constituting the core of the particles is prepared, then the polymer with a Tg of greater than 50 ° C constituting the shell is prepared. "hard".

Note that, in order for the particles to be perfectly structured, the mixture of monomers to be polymerized to form the core must be more hydrophobic than that to be polymerized to form the shell.

For each step, the polymerization reaction is preferably conducted under an inert atmosphere in the presence of radical initiators. The priming system used can be an oxidation-reduction system, a thermal or peroxidic system such as tert-butyl hydroperoxide / (sodium bisulfate) or di isopropyl benzene, the quantities used being between 0.2 and 1.0% by weight relative to the total mass of the monomers, preferably between 0.25 and 0.5% by weight.

The emulsion polymerization reaction according to the invention is carried out at a temperature between 25 and 150 ° C. and is a function of the nature of the initiation system used.

The preparation of the dispersions according to the invention is preferably carried out according to a semi-continuous type process making it possible to limit the drifts in composition which are a function of the differences in reactivity of the different monomers. The introduction of the monomers either pure or in the form of a pre-emulsion with part of the water and of the surfactants is thus generally carried out over a period of time from 3 hours 30 to 5 hours. It is also useful, although not essential, to seed 1 to 15% of the monomers. The emulsifying systems used in the emulsion polymerization process according to the invention are chosen from the range of emulsifiers having a suitable hydrophilic / lipophilic balance. The preferred systems are constituted by the association of an anionic surfactant, such as sodium lauryl sulfate, nonylphenol sulfates ethoxylated in particular with 20 - 25 moles of ethylene oxide, benzene dodecylsulfonate and ethoxylated fatty alcohols sulfates, and a nonionic surfactant, such as ethoxylated nonylphenols in particular with 10 - 40 moles of ethylene oxide and ethoxylated fatty alcohols.

Another object of the invention is a process for obtaining films for surface coatings.

This process consists in applying the latex of the invention as it is, without adding coalescing agents or volatile organic compounds, to any surface and allowing it to dry at a temperature between 0 and 40 ° C and preferably close to 25 ° C.

One of the objects of the invention is a process for obtaining a film for the treatment of different surfaces such as glass, leather, metal by drying at a temperature below 40 ° C. and preferably close to 25 ° C. of a latex. consisting of particles of polymers structured in the core / shell characterized in that the drying is carried out without the aid of coalescing agents or other volatile organic compounds.

The films of the invention can be used as binders in numerous applications, such as in paints, varnishes, surface treatment of glass, wood, leather or paper. They are formulated and / or loaded according to the intended application.

In addition, and for certain applications, the materials treated on the surface by the films of the invention may contain, on the side of said films, another material such as glass, paper, leather or an anti-reflection, anti-scratch or anti-ultraviolet film.

The following examples illustrate the invention without limiting it.

Example 1: preparation of a latex according to the invention

The operation is carried out in a 5 liter reactor equipped with an agitator, a temperature sensor and a double jacket through which a heat transfer fluid is passed to maintain the reactor at temperature.

1500 g of demineralized water and 4.8 g of disodium phosphate are introduced into this reactor, maintained at ambient temperature, and with stirring, after having carried out a degassing with nitrogen, and 40.05 g of lauryl sulfate are dissolved in this medium. sodium as an emulsifier.

The temperature of the contents of the reactor is then brought to 57 ° C. and, while maintaining this temperature, 991.75 g of n-butyl acrylate and 9.2 g of 1,4-butanediol diacrylate are then added simultaneously to said content.

The temperature of the reactor is brought to 66 ° C. and 1.3 g of potassium persulfate dissolved in 12.5 g of water and 0.925 g of sodium bisulfite dissolved in 35 g of water are added to the reaction medium.

After an induction time of approximately 15 minutes, the temperature rises to 107 ° C.

After this exotherm, a mixture consisting of 98.9 g of n-butyl acrylate and 5.48 g of diallyl maleate, then 0.15 g of potassium persulfate dissolved in 25 g of water is added to the reactor maintained at 80 ° C. The temperature is maintained at 80 ° C for one hour. The elastomeric core consisting of latex particles of Coulter diameter 77 nm is obtained with a conversion of 97%.

To the reaction medium obtained above, maintained at 80 ° C., 1 g of sodium formaldehyde sulfoxylate in 5 g of water is added, with stirring. Then added over a period of one hour 279.9 g of methyl methacrylate, and on the other hand 0.825 g of diisopropylbenzene hydroperoxide in 275 g of water.

The contents of the reactor are maintained at 80 ° C. for 1.5 hours after the start of the addition of methyl methacrylate, and 0.5 g of tert-butyl hydroperoxide and 0.175 g of sodium bisulfite are added to the content. 10 g of water.

The reaction mixture is then maintained at 80 ° C for one hour. At the end of this period, the contents of the reactor are cooled to room temperature.

A latex of the graft copolymer, the average particle diameter of which is 85 nm and the dry extract of 39.9%, is obtained with a conversion of 96.4%. Analysis of the polymer obtained shows that it has 2 Tg, one located at -38 ° C, the other at 105 ° C.

Examples 2 and 3

The procedure is the same as in Example 1, except that the composition of the monomers to be polymerized is modified at each stage so as to modify the Tg of the copolymers prepared.

The characteristics of the latex particles 2 and 3 of Examples 2 and 3 are as follows:

Latex 2: (example 2 according to the invention) average particle diameter: 90 nm

Tg1: -49 ° C

Tg2: 100 ° C.

Latex 2: (comparative example 3) average particle diameter: 90 nm

Tg1: -44 ° C

Tg2: 33 ° C.

Example 4 Preparation of an Unstructured Latex (Comparative)

In this example, the latex is unstructured because the polymer P2 is more hydrophobic than P1.

The procedure is the same as in Example 1 except that the methyl methacrylate is replaced by 279.9 g of styrene.

With a conversion of 99%, a latex is obtained, the average particle diameter of which is 81 nm and the dry extract of 40.15%.

Example 5 Preparation of a Mixture of Two Latexes, One of a Soft Character and the Other of a Hard Character (Comparative)

Preparation of a soft latex, polybutylacrylate (PABu)

The operation is carried out in a 2 liter reactor equipped with an agitator, a temperature sensor and a double jacket through which a heat transfer fluid is passed to maintain the reactor at temperature.

750 g of demineralized water and 2.4 g of disodium phosphate are introduced into this reactor, maintained at ambient temperature, and with stirring after degassing with nitrogen. 20.025 g of sodium lauryl sulfate as an emulsifying agent.

The temperature of the contents of the reactor is then brought to 57 ° C. and, while maintaining this temperature, 495.9 g of n-butyl acrylate and 4.6 g of 1,4-butanediol diacrylate are then added simultaneously.

The temperature of the reactor is brought to 66 ° C. and 0.4625 g of sodium bisulfite dissolved in 15 g of water and 0.65 g of sodium persulfate dissolved in 15 g of water are added to the reaction medium.

After an induction time of approximately 15 minutes, the temperature rises to 11 ° C. The reaction mixture is then maintained at 80 ° C for one hour. At the end of this period, the contents of the reactor are cooled to room temperature.

With a conversion of 99%, a latex is obtained whose average particle diameter is 82 nm and the dry extract is 36.90%.

Preparation of a hard latex, polymethyl methacrylate (PMMA)

We proceed in the same way as before except that we replace

750 g of water per 601 g

2.4 g of disodium phosphate per 1.76 g

20.025 g sodium lauryl sulfate per 14.7 g

495.9 g of n-butyl acrylate per 501.4 g of methyl methacrylate

4.6 g of butandiol diacrylate per 1.77 g of tetra dodecyl mercaptan

0.4625 g of sodium bisulfite per 0.24 g

0.65 g of potassium persulfate per 0.67 g.

A latex with an average diameter of 81 nm and a dry extract of 41.40% is obtained with a conversion of 99%.

The two latexes obtained are then mixed so as to have the final composition 80% by weight of polymer of soft character and 20% by weight of polymer of hard character.

Example 6: Preparation of film.

The latex from Example 1 is applied in thin layers on a glass plate and left to dry at room temperature. After evaporation of the water, a continuous, homogeneous film is obtained without surface tack. This 300 μm thick film is cut into rectangular plates 20 mm long and 4 mm wide. The rectangular plates underwent a mechanical tensile test at a speed of 10 mm per minute. The results obtained are as follows:

- module: 30 MPa - stress at the threshold: 0.7 MPa

- elongation at break: 150% Examples 7, 8, 9 and 10

The procedure is the same as for Example 4, but the latexes of Example 1 are replaced by those of Examples 2, 3, 4 and 5.

The films obtained underwent the same test as before. The results obtained are: for Example 7 (latex No. 2 according to the invention):

- flexible film without surface tack

- modulus of elasticity: 80 MPa

- threshold stress: 2 MPa

- elongation at break: 100% for Example 8 (comparative latex No. 3):

- flexible film having a surface tack

- modulus of elasticity: 3 MPa

- threshold stress: 0.45 MPa

- elongation at break: 300%. for example 9 (unstructured latex n ° 4: comparison):

- film with surface tights

- modulus of elasticity: 1 MPa

- threshold stress: 0.16 MPa

- elongation at break: 100%

- energy at break: 0.1 mJ / mm3 for example 10 (latex mixture n ° 5: comparison):

- modulus of elasticity: 2 MPa

- stress at the threshold: 0.2 MPa

- elongation at break: 100%

- energy at break: 0.1 mJ / mm3

- E 'less than 1 E + 7 (appendix 3) indicates the presence of surface tack.

Claims

1. Hydrophobic thermoplastic film having no surface tack consisting of 70 to 90% by weight of a polymer (P1) with a soft character having a Tg of less than 20 ° C dispersed in 10 to 30% of a polymer (P2 ) having a hard character having a Tg greater than 50 ° C., characterized in that the polymer P1 is dispersed in the form of individual nodules in the matrix constituted by the polymer P2.

2. Film according to claim 1 characterized in that P1 is more hydrophobic than P2.

3. Film according to one of the preceding claims, characterized in that P1 has a Tg of less than 0 ° C and P2 a Tg of more than 60 ° C.

4. Film according to one of the preceding claims, characterized in that P1 and P2 consist of 80% to 100% by weight of units derived by polymerization of at least one monomer chosen from group I consisting of:

- C1 -C8 (meth) acrylic acid esters

- conjugated dienes such as butadiene, isoprene

- acrylamide, methacrylamide and acrylonitrile

- vinyl chloride

- (meth) acrylic acids and their derivatives, and from 0% to 10% by weight of units derived by polymerization of at least one monomer chosen from group II consisting

- allylic esters of alpha, beta unsaturated carboxylic or dicarboxylic acids

- conjugated dienes such as butadiene, isoprene,

- allyl acrylates, allyl methacrylates,

diacrylates or dimethacrylates of diols such as ethylene glycol dimethacrylate, 1,3 butylene glycol dimethacrylate, 1,4 butanediol diacrylate, - polyvinylbenzenes such as divinylbenzene or trivinylbenzene,

- polyallylics such as diallyl maleate or triallyl maleate.

5. Film according to claim 4 characterized in that the preferred monomers are: for P1, butyl acrylate, ethyl acrylate, butadiene, butyl methacrylate, methyl methacrylate, among the monomers of the group I, butanediol 1.4 diacrylate, butadiene, ethylene glycol diacrylate, diallyl maleate, and allyl methacrylate among the group II monomers, and for P2, methyl methacrylate, butyl methacrylate, acid methacrylic among the group I monomers, and no group II monomer.

6. Latex containing neither coalescing agent nor volatile organic compounds, film-forming by evaporation at a temperature below 40 ° C and preferably close to 25 ° C, characterized in that said latex is based on particles of hydrophobic polymers structured in heart / bark and made up of:

7. Latex according to claim 6 characterized in that the core is more hydrophobic than the bark.

8. Latex according to one of claims 6 or 7 characterized in that the core has a Tg of less than 0 ° C and the shell a Tg of more than 60 ° C.

9. Latex according to one of claims 6 to 8 characterized in that the polymers are prepared in two stages, by emulsion polymerization of a mixture of monomers consisting of: from 90% to 100% by weight of at least one chosen monomer in group I, and from 0% to 10% by weight of at least one monomer chosen from group II.

10. Process for obtaining films of claims 1 to 5 by drying at a temperature below 40 ° C and preferably close to 25 ° C of a latex according to any one of claims 6 to 9 characterized in that the drying is carried out without the aid of coalescing agents or other volatile organic compounds.

11. A method of surface treatment of materials such as glass, leather, wood, paper, metals, characterized in that the method of claim 10 is applied to said materials.

12. Application of the films of claims 1 to 5 as binders in numerous applications, such as paints, varnishes, surface treatment of wood, leather or paper.

13. Surface such as glass, leather, metal, paper, wood, coated with the films of claims 1 to 5.

14. Surface according to claim 13 characterized in that it contains on the side of the films of claims 1 to 5 at least one other material such as an anti-reflection or anti-scratch film.